Functional Group Analysis of Reaction Products from Thermolysis of Lignin in Ethylene Glycol and Diethylene Glycol

Thermolysis of lignin in ethylene glycol and in diethylene glycol was studied. The experiments were carried out at 573 K and 623 K for 3 h. The reaction products of the thermolysis in ethylene glycol at 573 K and 623 K and in diethylene glycol at 623 K but not at 573 K separated into two liquid phases. The lower phase consisted of the glycol, major component, and water-soluble components, while the upper phase was a dark brown oil. Using the data from elemental analysis, ¹H-NMR, and ¹³C-NMR, the distribution of hydrogen and carbon was determined and the concentrations of 13 kinds of functional groups selected were determined from structural characterization analysis. Two methods were tested: the first (Method 1) used elemental analysis and ¹H-NMR data, while the second (Method 2) used not only elemental analysis and ¹H-NMR data but also ¹³C-NMR data. The two methods gave results considerably dissimilar for concentrations of functional groups containing an oxygen atom such as furan ring, glucose-unit secondary alcohol, and glucose-unit hemiacetal groups. This result may suggest that both ¹H-NMR and ¹³C-NMR data are indispensable for estimating the concentrations of these functional groups, which are the characteristics of lignin thermolysis oils. Method 2 is found to be superior for the structural characterization analysis of complex mixtures with high oxygen contents, e.g., lignin thermolysis oils and wood tars.